In general, a hydraulic excavator known as a representative example of a construction machine is configured of an automotive lower traveling structure, an upper revolving structure that is rotatably mounted on the lower traveling structure, and a working mechanism that is tiltably provided in an intermediate position in the left-right direction at a front side of the upper revolving structure. The upper revolving structure is configured of a revolving frame forming a support structure, a cab that is provided in a left front side of the revolving frame and is provided with an operator's seat on which an operator is seated, a right front housing cover that is positioned in a right front side at the opposite side in the left-right direction to the cab and is provided on the revolving frame to accommodate articles therein, an engine that is mounted in a rear side of the revolving frame, and a rear housing cover that covers the engine.
The working mechanism is configured of a boom a base end of which is tiltably connected to the revolving frame of the upper revolving structure, an arm that is rotatably connected to a tip end of the boom, a bucket that is rotatably connected to a tip end of the arm, and a boom cylinder, an arm cylinder and a bucket cylinder that respectively operate the boom, the arm and the bucket.
On the other hand, some of the working mechanisms adopt a two-piece boom in which the boom is divided into two pieces made of a first boom and a second boom for expanding a movable range thereof. The two-piece boom is configured of a first boom a base end of which is rotatably connected to the revolving frame, a second boom that is rotatably connected to a tip end of the first boom, a boom cylinder that is provided between the revolving frame and the tip end of the first boom to be positioned ahead of the base end of the first boom for lifting and tilting the first boom to the revolving frame, and a positioning cylinder that is provided between the first boom and the second boom to be positioned in front of the first boom for adjusting a folding angle of the second boom to the first boom, wherein the arm is rotatably connected to the tip end of the second boom.
The working mechanism with a two-piece boom specification rotates the second boom to the first boom by the positioning cylinder, thus making it possible to adjust the folding angle of the second boom to the first boom as needed. In a case where the excavating operation is performed by using the working mechanism, the movable range of the working mechanism can be widened by adjusting the folding angle between the first boom and the second boom corresponding to the excavating depth.
Further, some of the hydraulic excavators are provided with a wheel type lower traveling structure in such a manner as to be able to travel on a public road. At the traveling of the hydraulic excavator, the working mechanism takes a traveling stance where the boom cylinder is expanded to rotate the tip end of the first boom to the rear side and the positioning cylinder is compressed to rotate the tip end of the second boom to the lower side. At the time of putting the working mechanism to the traveling stance thus, the entire working mechanism can be folded in a compact manner to facilitate a driving operation of the working mechanism. On the other hand, a range of vision in the right side of an operator who drives the hydraulic excavator in the cab is widened by arranging the tip end of the first boom to be in the rear side (for example, Patent Document 1).